The present invention is directed to an implant and a configuration for implantation of the implant into the human body, especially along the spine, having improved stabilization and locking with respect to desired position of the overall implant, as well as improved resistence to torsion during use.
The art of correcting back deformities, injuries and the like has advanced dramatically in recent years. Surgeons who perform operations on the spine and related bones of the body are constantly developing new procedures and techniques that require implants which are capable of being stable in the body after implantation and which firmly lock in place so as to resist the substantial pressures and forces developed by the body on the implant. Such implants must often also resist twisting or torsion applied to parts of the implant and prior art implants have not always been successful at resisting twisting or torsion.
Such implants often involve rods which are placed along the spinal column or various bones of the living body and, once secured to the bones, such rods may be bent and shaped to force the bones to align with the rods and, in this manner, either provide correction to the bones caused by deformity, injury or the like. That is, one or more rods are placed in the correct curvature for the spine and the spinal bones are joined to the rod or rods, before or after bending the rods, in such a manner as to thereafter force the bones to follow the same configuration as the rods. Once the rods are bent, forces created by the muscles of the patient, or by sudden movement, or by accident, or the like often act to try to rotate or apply torque to the implant as a whole or a rod individually. That is such forces generally apply torsion to the apparatus. Such torsion may act to loosen or even dislodge the implant or to turn or rotate one or more rods to a less effective support position. It is desirable that the apparatus be able to resist such forces acting upon it.
Historically, the rods used as implants in the manner described above, are typically joined with various bones along the length of the rod by use of bone screws or other implants that are joined with the rod. It has been found that conventionally available implants have systems that join rods to bone screws or intermediate connectors in such a manner that the rods are often held against axial movement relative to the bone screws or intermediate connector. That is, the rods are not likely to move substantially with respect to the other implants in a direction that is along the central axis of the rod. However, because of the substantial forces exerted on the rod during use, certain forces act to try to rotate the rod within bone screws and connectors, such that the spinal corrective configuration and positioning of the rod can slip due to rotation of the rod from an optimal position to one that is less suited for the patient. This can occur when substantial forces are applied to the back during exercise, accident or the like.
Consequently, it is desirable to have an implant that not only effectively resists axial movement of the rod relative to the other implants, but also effectively resists torque or torsion that produce turning of the rod or rotation of the rod relative to the implants. One use of the present invention is especially suited for the locking and stabilizing an anterior spinal implant. In particular, the installation of anterior spinal rods is often utilized to reposition the spine and correct deformities and the like. Such a rod is typically anchored at opposite ends to vertebrae and is likewise joined with vertebrae along the length of the rod by bone screws or the like. Such a system is typically installed by curving the rod to fit the malformed spine of the patient and then securing the anchors at both ends and various intermediate bone screws to the rod. The rod is thereafter bent by rod benders to assume the desired configuration of the spine and the rod in this manner translates the various bones of the spine along with it to the correct configuration.
Once the rod is bent, the body exerts a substantial amount of rotational force or torsion on the rod, especially should the patient be struck on the back, during exercising, or the like. It is also noted that the rod can first be bent and then the bone moved to the rod and secured to the rod. In either case, it is important that the anchors at opposite ends of the rod resist rotation of the rod therein and that the anchors themselves remain stable and securely attached to an associated bone. Furthermore, it is important to both lock the rod against rotation in or relative to the bone screw and to secure the anchors of the rod against rotation relative to the spine.
An implant system is therefore desirable that provides a strong anchor at opposite ends of the rod that resists rotation of the rod both relative to the bone screws and relative to the spine during procedures at the time of implantation and later during use.